The present invention relates generally to a cooling device including a heat spreader for removing heat from a component connected with the cooling device. More specifically, the present invention relates to a cooling device that includes a heat spreader made from a dissimilar material with a higher thermal conductivity than a material of a heat mass of the cooling device so that heat in a component connected with the cooling device is efficiently removed.
It is well known in the electronics art to place a heat sink in contact with an electronic device so that waste heat generated by operation of the electronic device is thermally transferred to the heat sink thereby cooling the electronic device. With the advent of high clock speed electronic devices such as microprocessors (xcexcP), digital signal processors (DSP), and application specific integrated circuits (ASIC), the amount of waste heat generated by those electronic devices and the operating temperature of those electronic devices are directly proportional to clock speed. Therefore, higher clock speeds result in increased waste heat generation which in turn increases the operating temperature of the electronic device. However, efficient operation of the electronic device requires that waste heat be continuously and effectively removed.
Heat sink devices have become commonplace as a means for dissipating waste heat from electronic devices such as the types described above. In a typical application, a component to be cooled is carried by a connector that is mounted on a PC board. A heat sink is mounted on the component by attaching the heat sink to the connector using a clip or fasteners, for example. Alternatively, the heat sink is mounted to a PC board that carries the electronic device and fasteners or the like are used to connect the heat sink to the PC board via holes that are drilled in the PC board.
The need to drill holes can be one disadvantage to using fasteners because the fasteners or other mounting hardware used for connecting the heat sink to the PC board are usually electrically conductive and there is a risk of an electrical short due to contact between a PC board trace and the mounting hardware. Moreover, to avoid electrical shorts, the PC board traces can be routed around the hole, but that routing requires keep out zones that can complicate the routing of the traces.
Typically, a heat sink used in conjunction with a modem high clock speed electronic device will use an electrical fan mounted on top of the heat sink or within a cavity formed by cooling fins/vanes of the heat sink. The cooling fins increase the surface area of the heat sink and maximize heat transfer from the heat sink to ambient air that surrounds the heat sink. The fan causes air to circulate over and around the cooling fins thereby transferring heat from the cooling fins into the ambient air.
As mentioned previously, with continuing increases in clock speed, the amount of waste heat generated by electronic devices has also increased. Accordingly, to adequately cool those electronic devices, larger heat sinks and/or larger capacity fans (i.e. in CFM) are required. Increasing the size of the heat sink results in a greater thermal mass and a greater surface area from which the heat can be dissipated. Increases in fan capacity provide for more air flow through the cooling fins.
There are disadvantages to increased fan and heat sink size. First, if the size of the heat sink is increased in a vertical direction (i.e. in a direction transverse to the PC board), then the heat sink is tall and may not fit within a vertical space in many applications, such as the chassis of a desktop computer. Second, if the PC board has a vertical orientation, then a heavy and tall heat sink can mechanically stress the PC board and/or the electronic device resulting in a device or PC board failure.
Third, a tall heat sink will require additional vertical clearance between the heat sink and a chassis the heat sink is contained in to allow for adequate air flow into or out of the fan. Fourth, if the heat sinks size is increased in a horizontal direction, then the amount of area available on the PC board for mounting other electronic devices is limited. Fifth, when the heat sink has a cylindrical shape formed by the fins it is often not possible to mount several such heat sinks in close proximity to each other because air flow into and out of the fins is blocked by adjacent heat sinks with a resulting decrease in cooling efficiency.
Finally, increases in fan size to increase cooling capacity often result in increased noise generation by the fan. In many applications such as the desktop computer or a portable computer, it is highly desirable to minimize noise generation. In portable applications that depend on a battery to supply power, the increased power drain of a larger capacity fan is not an acceptable solution for removing waste heat.
In the above mentioned heat sink with cooling fins there are additional disadvantages to mounting the fan within a cavity formed by the fins. First, a substantial portion of a heat mass of the heat sink is partially blocked by the fan because the fan is mounted directly on the heat mass and therefore blocks a potential path for heat dissipation from the heat mass because air from the fan does not circulate over the blocked portion of the heat mass.
Second, without the fan, a depth of the fins could extend all the way to a center of the heat mass; however, the depth and surface area of the fins is reduced by a diameter of the fan because the fan is mounted in a cavity having a diameter that is slightly larger than the fans diameter to provide clearance for the fan blades. Consequently, the heat mass of the heat sink must be made broader to compensate for the reduced surface area of the fins. The broader heat mass increases the size, cost, and weight of the heat sink.
Third, the reduced depth of the fins makes it easier for the fins to be bent if damaged. One possible consequence of a bent fin is that it will contact and damage the fan blades and/or cause the fan to stall thereby damaging the fan or causing the fan to fail. Fourth, because the fan is mounted in the cavity formed by the fins, power leads for the fan must be routed through a space between the fins. Sharp edges on the fins can cut the power leads or cause an electrical short. In either case, the result is that the fan will fail. Fifth, glue is typically used to mount the fan to the heat sink and the glue can get into the fan and cause the fan to fail. Any of the above mentioned fan failure modes can lead to a failure of the electronic device the heat sink was designed to cool because air circulation generated by the fan is essential to effectively dissipate waste heat from the electronic device.
Some prior heat sinks attempt to overcome the aforementioned disadvantages of a larger heat mass or increased fin area by using a metal heat spreader that is joined with the heat sink. Typical processes for joining the heat spreader with the heat sink include brazing, soldering, heat shrink fitting, vacuum brazing, micro forging and shrink fitting.
One disadvantage of those processes is that they are very expensive resulting in a higher cost for the heat sink. Another disadvantage is that the above processes are limited in their ability to join dissimilar metals for the heat sink and the heat spreader, particularly if the metal for the heat spreader has superior thermal conductivity properties over the metal for the heat sink. A disadvantage of the shrink fitting process is that a thermal resistance between the heat spreader and the heat sink is high due to micro gaps between the heat spreader and the heat sink. Finally, depending on the application, another potential disadvantage to the above processes is that once joined, the heat sink and the heat spreader cannot be easily removed for servicing or for a field upgrade to a better material for the heat spreader.
Consequently, there is a need for a cooling device with a heat spreader that allows for the use of dissimilar materials that are optimized for efficient thermal conduction and heat dissipation. There is also a need for a cooling device with a heat spreader that eliminates micro gaps between the heat spreader and a heat mass so that there is a low thermal resistance between the heat spreader and the cooling device. There is a need for a cooling device with a heat spreader that provides an inexpensive processes for joining the heat spreader with the cooling device. There exists a need for a cooling device with dissimilar materials for the heat mass and the heat spreader that allows the heat spreader to be fixedly connected with the heat mass to prevent the heat mass and the heat spreader from separating from each other. Finally, there exists a need for a cooling device with a heat spreader that allows for easy disassembly and in field servicing.
Broadly, the present invention is embodied in a cooling device for dissipating waste heat from a component to be cooled. The cooling device includes a heat mass made from a first material and including a base, an arcuate boss that is surrounded by an arcuate groove, a taper bore extending from the base to the boss, and an aperture extending from the boss to the taper bore. A fastener including a head and a threaded shaft is inserted through the aperture with the head in contact with the boss. A heat spreader made from a second material that is dissimilar to the first material includes a taper wall that complements the taper bore of the heat mass, a mounting surface adapted to thermally connect with the component, a threaded aperture adapted to receive the threaded shaft of the fastener. Optionally, a thermal sealant is connected with the taper wall and/or the taper bore.
The heat spreader is inserted into the taper bore and the threaded shaft is threaded into the threaded aperture and the head of the fastener is turned to urge the taper wall into contact with the taper bore. The optional thermal sealant is operative to seal micro gaps between the taper bore and the taper wall so that a thermal resistance between the heat mass and the heat spreader is reduced.
Extending from the heat mass are a plurality of vanes that are spaced apart from each other to define a primary slot between adjacent vanes and extending to the heat mass. The vanes have a surface area that increases in a radially outward direction from an axis of the heat mass and a portion of the surface area of the vanes also increase in a direction that is along the axis. The vanes include a top face upon which a fan can be mounted, an aerodynamically profiled inner wall that defines a chamber that surrounds the boss and the groove, and an outer wall including a surface profile that widens from the base to the top face and includes a smooth curved portion, a draft portion, and a smooth radially outward portion. Furthermore, the surface area of the vanes is increased by a plurality of fins formed in each vane by a secondary slot extending through a portion of the vane.
An air flow entering the chamber creates a three-dimensional air flow that dissipates heat from the cooling device. First, the air flow exits through the vanes and a portion of the fins in an exhaust flow that dissipates heat from the vanes and the fins. Second, the exhaust flow creates a low pressure region within the chamber that induces an intake flow into the chamber through a major portion of the fins and a top portion of the vanes thereby dissipating heat from the fins and the vanes. Third, the low pressure region induces a surface flow along the inner wall so that the surface flow wets the groove and the boss as it passes over the groove and the boss to dissipate heat from the heat mass.
The cooling device of the present invention solves the aforementioned disadvantages of prior heat sinks. The cooling device can be mounted to a component to be cooled by using a clip to connect the cooling device with a connector that carries the component. Therefore, holes need not be drilled in a PC board to mount the cooling device. The cooling device employs vanes that extend deep within the heat mass and the surface area of the vanes increases from a bottom of the cooling device to a top of the cooling device and in a radially outward direction from the heat mass. Furthermore, each vane is split into at least two fins thus further increasing the surface area available for cooling. As a result, the cooling device need not be made taller to increase vane surface area and the cooling device need not be made wider to increase the size of the heat mass.
The top of the cooling device is adapted to mount a fan so that the heat mass is not blocked by the fan and air can circulate over the heat mass thus further dissipating heat from the cooling device. The fan can include a shroud that surrounds the blades unlike the fans that are mounted in a cavity formed by fins of prior heat sink devices. However, the cooling device can also mount a fan without a shroud using a clip or space frame to mount the fan to the top of the cooling device. Because the fan is mounted on top of the cooling device, the wires of the power leads for the fan are not routed through the vanes or fins thereby eliminating the risk of the wires being cut or short circuited.
The shape of the cooling device (wider at the top than at the bottom) allows for several of the cooling devices to be placed adjacent to each other without blocking air flow into and out of the vanes and fins.
The vanes of the cooling device can be tangentially oriented with a circle centered on an axis of the heat mass and the vanes can be inclined at an angle with respect to the axis such that the angle of inclination substantially matches or closely approximates a pitch angle of the blades of a fan. The tangential orientation and the inclination of the vanes reduces fan noise due to air shock losses.
The heat spreader can be mounted with the heat mass using a fastener or the like thereby eliminating the problems and costs associated with the prior welding or brazing of dissimilar metals to each other. Additionally, the use of the fastener allows for easy in field servicing, repairs, and upgrades to the cooling device. Furthermore, if necessary, the heat spreader can be fixedly connected with the heat mass by preventing removal of the fastener and/or by welding, brazing, soldering the heat spreader to the heat mass.
Moreover, a second material for the heat spreader can be selected for its superior thermal conductivity properties for efficient conduction and dissipation of waste heat from the component connected with the mounting surface of the heat spreader. Furthermore, the optional thermal sealant of the present invention solves the aforementioned problems caused by micro gaps between prior heat spreaders and heat sinks by sealing those micro gaps thereby reducing a thermal resistance between the heat spreader and the heat mass.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the present invention.